Because grasses and shrubs may induce different spatial distributions of nutrients in desert soils, this study was initiated to examine the redistribution of nitrogen in grassland and shrubland soils over a long time period. The stable isotope N15 was applied to plots in grassland and shrubland, and the plots were measured annually from 1989-1993 and again in 1999, 2001, and 2002.

Plot establishment - We established four 10 X 10-m plots in grassland and shrubland habitats near the Five Points area of the Sevilleta Long Term Ecological Research Site (LTER) in the northern Chihuahuan Desert, New Mexico, USA.

In the grassland, paired plots (two plots separated by 50-m) were located at sites where Bouteloua eriopoda (Torr.) Torr. (Black grama) and B. gracilis (H.B.K.) Lag. ex Steud. (Blue grama) dominate. In the shrubland, paired plots were located in areas dominated by Larrea tridentata D.C. (Cov.)(creosotebush).

Tracer application - 15NH4Cl tracer was applied to ten 15.25 cm diameter points arranged in a stratified random design in each of the four 10 X 10 m plots in the grassland and shrubland. 0.33 g of 15NH4Cl were dissolved in 500 ml of deionized water and applied to ten sites per plot in 50 mL aliquots in July, 1989.

Sampling - The site of each spike application was sampled annually during the summer in 1989, 1990, 1991, 1992, and 1993. Two samples with a volume of 28.5 cubic centimeters were removed from the site of spike application, which had a total volume of 1815 cubic centimeters to 10-cm depth. Each sample contained a small percents of the total soil volume, about 1.5 percent. All samples were air-dried, sieved through a 2 mm sieve, and shipped to Duke University. Ground soil samples were analyzed for 15N.

Field collections were made every even-numbered month as close to the 15th as possible.

The samples taken in 1989-1993 and 1999 were analyzed by Larry Giles on a mass spectrometer at the Duke University

This specific monitoring location is about 650 m up the Abeja channel from the previous location. Here bedrock forces any streamflow to the surface. There is also a spring at this location from which water originates during relatively wetter periods

The varied topography and large elevation gradients that characterize the arid and semi-arid Southwest create a wide range of climatic conditions - and associated biomes - within relatively short distances. This creates an ideal experimental system in which to study the effects of climate on ecosystems. Such studies are critical givien that the Southwestern U.S. has already experienced changes in climate that have altered precipitation patterns (Mote et al. 2005), and stands to experience dramatic climate change in the coming decades (Seager et al. 2007; Ting et al. 2007).

The varied topography and large elevation gradients that characterize the arid and semi-arid Southwest create a wide range of climatic conditions - and associated biomes - within relatively short distances. This creates an ideal experimental system in which to study the effects of climate on ecosystems. Such studies are critical givien that the Southwestern U.S. has already experienced changes in climate that have altered precipitation patterns (Mote et al. 2005), and stands to experience dramatic climate change in the coming decades (Seager et al. 2007; Ting et al. 2007). Climate models currently predict an imminent transition to a warmer, more arid climate in the Southwest (Seager et al. 2007; Ting et al. 2007). Thus, high elevation ecosystems, which currently experience relatively cool and mesic climates, will likely resemble their lower elevation counterparts, which experience a hotter and drier climate. In order to predict regional changes in carbon storage, hydrologic partitioning and water resources in response to these potential shifts, it is critical to understand how both temperature and soil moisture affect processes such as evaportranspiration (ET), total carbon uptake through gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange of carbon, water and energy across elevational gradients.

We are using a sequence of six widespread biomes along an elevational gradient in New Mexico -- ranging from hot, arid ecosystems at low elevations to cool, mesic ecosystems at high elevation to test specific hypotheses related to how climatic controls over ecosystem processes change across this gradient. We have an eddy covariance tower and associated meteorological instruments in each biome which we are using to directly measure the exchange of carbon, water and energy between the ecosystem and the atmosphere. This gradient offers us a unique opportunity to test the interactive effects of temperature and soil moisture on ecosystem processes, as temperature decreases and soil moisture increases markedly along the gradient and varies through time within sites.

This file contains data collected from 1996-1999 at a Bowen ratio tower adjacent to the Deep Well Meteorological Station at Deep Well (Station 40). The Bowen ratio method employs a method of measuring the temperature and vapor pressure gradient over a vegetation canopy to quantify evapotranspiration from that canopy.

Keywords:

measurements

vapor pressure

humidity

relative humidity

wind

temperature

fluxes

heat flux

methods

soil

Purpose:

The data was collected to identify the daily patterns of evapotranspiration from the surrounding area.

Additional Information:

When the Samples/Data were Collected:

The data were collected spring, summer, and fall of each year when the instrument was operating properly. For 1996 the period of collection was Julian day 1 (Jan 1) through 183. For 1997 the period of collection was Julian day 118 (Apr 27) through 290 (Oct 17) with some missing periods due to equipment problems - see mainentance log. For 1998 the period of collection was Julian day 84 (Mar 25) through 274 (Oct 1). For 1999 the period of collection was Julian day 99 (Apr 9) through 123 (May 3) and day 147 (May 27) through day 315 (Nov 11). Data were measured over 20 minute periods and means, totals, and instantaneous readings were output at the hour, 20 min. and 40 min. past the hour for the preceeding 20 minutes.

Where the Data were Collected:

Sevilleta LTER Project Area Description

McKenzie Flats, Deep Well Meteorological Site

Latitude 34.3586 Longitude -106.6911

Study Area Description:

The study area is about halfway between Black Butte and Five Points. It is about 200 m west of the road site

Location Description:

The area around the station can be classified as desert grassland, dominated by black grama (Bouteloua eriopoda) and blue grama grass (B. gracilis), with lesser amonts of various drop seeds and sacatons (Sporobolus spp.), purple three-awn (Aristida purpurea), and Pleuraphis jamesii. The sub-shrub snakeweed (Gutierrezia sarothrae) is common during wet years and there are a few creosote bushes (Larrea tridentata) and four-wing salt bushes (Atriplex canescens) in the vicinity.

Descriptors Soil:

Berino Series: The soils in the Berino series are classified as fine-loamy, mixed, thermic Typic Haplargids. These form well drained, moderately permeable soils formed in alluvial and eolian material. They are on bajadas, plains, and broad fan terraces.

Slope/Aspect: Approximately 1-2%, westerly aspect.

Vegetation Community: Mixed-species desert grassland.

Terrain/Physiography: McKenzie Flats is a broad, nearly flat grassland plain between the Los Pinos Mountains and the breaks on the east side of the Rio Grande.

Hydrology - surface/groundwater: Surface water is present only during rainfall events (particularly summer thunderstorms). Area is considered a "run-on" plain for watersheds of the Los Pinos Mountains. No major arroyos are present on the study area, although Palo Duro Canyon borders the southern part of the study area.

Size: McKenzie Flats encompasses an area of approximately 50 square miles.

Elevation: 1600 m (5249 ft)

Climate (general): The McKenzie Flats area of the Sevilleta NWR has one of the LTER weather stations located in the central part of the flats. This is the Deep Well station. For climate details and data, consult the Sevilleta Meteorology databases.

The Bowen ratio method measures the gradient of temperature and moisture above a typical canopy. In conjunction with measuring incoming net radiation, this method can partition the energy into soil heating, atmospheric heating (specific heat) and evaporation as latent heat.

A Bowen ratio station includes a 3 m tower on which is mounted most of the following sampling equipment: an enclosure, which houses a datalogger, and a gas flow system which directs air from upper and lower arms of the station to the cooled mirror hygrometer. On the tripod are upper and lower arms with mountings for thin wire thermocouples and intakes for air samples. A set of 4 temperature probes are buried in the top 10 cm of the soil with readings taken at 2 and 8 cm. One pair of probes is located under a clump of grass while a second is in unvegetated soil. Two soil heat flux plates are buried at a depth of 10 cm, again one under vegetation and one in the open. A net radiometer is mounted on a pipe about 1 m above the soil surface. A wind sentry, which includes both an anemometer and wine vane, is mounted at a height of 3 m.

Global climate change processes, especially prolonged droughts and increasingly high temperatures, are significantly affecting numerous arid ecosystems across the state of New Mexico. One of the more adversely affected ecosystems in New Mexico is piñon-juniper woodland (PJ), which includes areas near Mountainair, New Mexico, USA. Because changes in ambient temperature and decreases in water availability show pervasive effects on the above-ground status of existing PJ woodlands in New Mexico, it seems likely that the effects of changes in these two master variables will manifest themselves within soil processes such as soil organic matter (SOM) decomposition rates and soil respiration rates, as well as nutrient cycling rates and availabilities to both plants and soil microbial communities.

We conducted analyses of soil physicochemical properties and soil fungal biomass via soil ergosterol content, as well as evaluating the activity rates of multiple hydrolytic exoenzymes, which are indicative of fungal activity in soils. Samples were collected from multiple tree-to-tree competition gradients that were identified in May/June of 2011. These gradients were established based on the type of mycorrhizal fungus types expected to occupy the soil community established beneath the canopy of a focal tree, with there being two focal trees in each gradient. Gradients were established between two live piñon trees (Pinus edulis), two juniper trees (Juniperus monosperma), a live piñon and live juniper, and a dead piñon and live juniper. We only sampled from under live trees at the control site.

In order to obtain these samples, we collected soil samples from two different sites in a PJ woodland located within the boundaries of the Deer Canyon ranch. Changes in soil conditions were captured by sampling from the two sites at multiple times throughout the summer of 2011. We collected samples from Dr. Marcy Litvak’s girdled PJ woodland eddy-flux tower site in June, July, August and finally in late September. We also collected samples from Dr. Litvak’s control PJ woodland tower site in June and September of 2011. Significant differences in the activity rates of the hydrolytic exoenzymes alanine aminopeptidase, alkaline phosphatase, β-d-glucosidase, and β-N-acetyl glucosaminidase were observed within soils collected at multiple times from June through September when comparing the observed rates of activities under the trees in the live piñon to live piñon gradients vs. the juniper to juniper gradients. These differences were observed in samples from multiple dates at the girdled site without there being significant differences in soil fungal biomass across seasons or study sites. Continued work with the established sites on a year-to-year basis could provide an insight into how the fungal communities within New Mexican PJ woodlands will respond to future changes in soil conditions as global climate change processes advance in New Mexico.

Experimental design:Randomized complete block design was established at 2 different study sites, girdled piñon-juniper (PJ) woodland and non-girdled (control) PJ woodland.In late May, 2011, we set-up each study site to contain six complete blocks (plots), each with multiple tree-to-tree gradients. At the girdled PJ site, each plot included five different tree-to-tree gradients: Live pine to live pine, live pine to dead pine, live pine to live juniper, dead pine to live juniper, and live juniper to live juniper.At the control PJ site we also established 6 blocks (plots); however, at this site there were only three gradients: Live pine to live juniper, dead pine to live juniper, and live juniper to live juniper.

Setting up plots:Plots and gradients were established by marking sampling locations with orange flagging tape and pin-flags by Daniel Warnock and Kimberly Elsenbroek on May 19 and 23, 2011.

Sample collection, allocation and storage: Soil samples were collected monthly from the girdled PJ woodland to establish two pre-monsoonal (dry) season time points, with samples collected on June 6, 2011 and June 15, 2011 considered as being from single time point.Soil samples collected on July 20, 2011 represented our second dry season time point.Soil samples for our two post-monsoon moisture time points were collected on August 15, 2011 and September 28, 2011. As with the girdled site, soils sample from the control PJ woodland site were collected both before and after the onset of the monsoon season.However, unlike the girdled PJ woodland site, we only have one pre-monsoon time point June 29, 2011 and one post monsoon time point, September 15, 2011.

All soil samples were collected by combining three 0-10cm sub-samples into the same zipper-locking plastic storage bag.Samples were collected from three different locations within each tree-to tree gradient.Two of the three samples were collected from locations within 30cm of the trunk of each of the two focal trees within a gradient.The other sample for each gradient was collected from a point at the center of a zone formed by the edges of the canopies from the two competing focal trees.All samples were then transported to the lab for refrigeration.

Within 24-72 hours of sample collection, 5mL sub-samples were taken from each bulked soil sample and placed into individual Corning 15mL screw-cap centrifuge tubes.Each tube was then filled to the 10mL mark with an 0.8% KOH in Methanol solution.These tubes were placed in the fridge for storage until analyzed for ergosterol content. After preparation of the samples for ergosterol analyses, 1g samples were placed into 125mL round Nalgene bottles for analyses of fungal exoenzyme actitity (EEA) rates from each sample.All enzyme activity assays were performed within 1 to 5 days after collection. Further, for all but the final post-monsoonal time points, assays were performed within 2 to 3 days of sample collection.

After all of the fresh, refrigerated samples were alloquated for ergosterol and EEA analyses we placed the remaining quantities of soil for each sample into labeled paper bags for air-drying on a lab bench.After 1-2 weeks, 30g of each sample was placed into a labeled plastic bag for shipping to Ithaca, New York, USA for analyses of soil-physicochemical properties.While taking the 30g sub-samples, a separate 5g sub-sample from the air-dried sample was placed into a labeled, no. 1 coin-envelope for storage until analysis of soil hyphal abundance. After all sub-sampling was completed any remaining soil was kept in its sample bag and stored in the lab.

Hydrolytic exoenzyme activity (EEA) assays:All hydrolytic EEA assays were performed as follows:Each 125mL sample bottle was partially filled with 50mM sodium bicarbonate buffer solution and homogenized using a Kinematica Polytron CH 6010 (Lucerne, Switzerland).Upon homogenization, sample bottles were filled to 125mL with buffer solution.Sample bottles were then set aside until placement in black, 96-well, micro-plates.At the time of placement, each sample suspension was poured into a glass crystalizing dish where it was stirred at high speed into the appropriate columns within each micro-plate.These columns included a quench control (200 uL sample suspension + 50uL MUB or methylcoumrin substrate control), a sample control (200uL sample suspension + 50uL 50mM bicarbonate buffer) and an assay column (200uL suspension + 50ul 200mM substrate).Samples were pipetted into four sets of plates with each set analyzing the activity rates of a single hydrolytic enzyme.These enzymes included alanine amino peptidase, alkaline phosphatase, β-d-glucosidase, and N-acetyl-β-d-glucosiminidase.Further, all three samples from a single gradient within a single plot were added to the same plate (e.g., all samples from the live-pine-to-live-pine gradient from plot one were pipetted into a single plate for analyzing the activity of the enzyme alkaline-phospotase.

Ultimately our plate layout was completed as follows usingt two other columns for substrate controls:In column one, we added 200uL buffer and 50uL of a substrate standard, which accounts for the fluorescence emitted by either the MUB, or the methylcoumarin group that is a component of the substrate solution added to the assay wells.In column six of each plate was a substrate control, which is a solution of 200uL buffer and 50uL of one the four different substrates used in our hydrolytic EEA assays.Columns 3-5 were our quench controls, which accounts for the quantity of fluorescence emitted by the MUB or methylcoumarin molecule absorbed by the particles in the soil suspension itself.Columns 7-9 were the sample controls and account for the amount of fluorescence emitted by the soil suspension + buffer solution added to each well.Finally, columns 10-12 were our assay wells.From these wells we could determine enzyme activity by measuring the fluorescence emitted by the MUB or methylcoumarin molecules cleaved off of the substrates initially added to each well.The substrates included in these assays included: 7-amino-4-methylcoumarin (Sigma-Aldrich), 4-MUB-phosphate (Sigma-Aldrich), 4-MUB-β-d-glucoside (Sigma-Aldrich), and 4-MUB-N-acetyl-β-d-glucosiminide (Sigma-Aldrich).

Because the intrinsic EEA rates varied across our targeted exoenzymes, assay plates were scanned for flourscence in sets of two.Alanine aminopeptidase plates and alkaline phosphatase plates were scanned twice, first at 30-40 minutes after substrate addion and again at 50-80 minutes after substrate addition.β-d-glucosidase, and N-acetyl-β-d-glucosiminidase plates were all scanned at 3-4 hours after substrate addition.The timing of the second enzyme activity time point depended on expected soil moisture conditions.Here, the post monsoon soils were allowed to incubate for a total of 5-6 hours prior to the second scan and the pre-monsoon plates were incubated for a total of 7-9 hours.

Fungal biomass measurements: Fungal biomass was quantified by measuring the concentration of ergosterol in a sub-sample taken from each soil sample collected from June to September.Within 24-72 hours of sample collection, 5mL sub-samples were taken from each bulked soil sample and placed into individual Corning 15mL screw-cap centrifuge tubes.Each tube was filled to the 10mL mark with an 0.8% KOH in methanol solution.Tubes were refrigerated for storage until analyzed for fungal biomass by measuring the ergosterol content within each sample.Ergosterol concentration for each sample was determined using HPLC with 100% methanol as the solvent at a flow rate of 1.5mL/ minute and a c-18 column.Ergosterol was quantified by measuring the peak height that passed through a detector set to measure absorbance at 282nm, at 3.7min after the sample was injected into the column.The height of each peak was then converted into μg ergosterol/g soil and finally converted to mg fungal biomass/ g soil by applying a conversion factor.

Instrumentation:

I

* Instrument Name: Polytron

* Manufacturer: Kinematica

* Model Number: CH 6010

* Instrument Name: GeoXT

* Manufacturer: Trimble

* Model Number: GeoExplorer 3000 series

* Instrument Name: fmax

* Manufacturer: Molecular devices

* Model Number: type 374

* Instrument Name: versamax tunable micro-plate reader

* Manufacturer: molecular devices

* Model Number: ?

* Instrument Name: SSI 222D isocratic HPLC pump

* Manufacturer: SSI

* Model Number: 222D

* Instrument Name: Thermo Seperation Products AS 1000 autosampler

* Manufacturer: Thermo Seperation Products

* Model Number: AS 1000

* Instrument Name: Acutect 500 UV/Vis Wavelength detector

* Manufacturer: Acutect

* Model Number:500

* Instrument Name: HP 3396 series iii integrator

* Manufacturer: Hewlitt Packard

* Model Number: 3396

restricted:

Access to Data is Restricted per LTER Data Sharing Policy. Contact SEV IM for more information.

Dryland environments are estimated to cover around 40% of the global land surface, and are home to approximately 2.4 billion people. Many of these areas have recently experienced extensive land degradation. This study focuses on semi-arid areas in the US Southwest, where degradation over the past 150 years has been characterized by the invasion of woody vegetation into areas previously dominated by grasslands. This vegetation change has been associated with increases in soil erosion and water quality problems, including the loss of key nutrients such as carbon from the soil to adjacent fluvial systems. Such loss of resources may impact heavily upon the amount of carbon that is lost as the land becomes more heavily degraded.

Therefore, understanding these vegetation transitions is significant both for sustainable land use and global biogeochemical cycling. This study uses an ecohydrological approach to develop an understanding of the relationship between structure and function across these transitions. This is done via the monitoring of rainfall-runoff events across instrumented runoff plots with different vegetation characteristics to investigate fluvial sediment fluxes during intense summer monsoon season rainfall events.

Keywords:

events

precipitation

rain

cores

carbon

water

runoff

deserts

grasslands

grasses

vegetation

Additional Information:

This data was collected and analyzed by Alan Puttock as part of the PhD project: ‘Developing an understanding of vegetation change and fluvial carbon fluxes in semi-arid environments’. This project is supervised by Dr Richard Brazier, Dr Jenifer Dungait and Dr Kit Macleod. Analysis of samples/data is being carried out at the University of Exeter and North Wyke Research, United Kingdom.

This data was collected under USFWS permit number: 22522 10-026

Study Area 1:

Study Area Name: Grass Endmember Plot

Study Area Location: Five Points Grass core site (exact point location of plot provided below)

Single Point:

North Coordinate: 34.339186

West Coordinate: -106.728303

Study Area 2:

Study Area Name: Creosote Endmember plot

Study Area Location: Five Points Creosote core site (exact point location of plot provided below)

Each study area consisted of a 10m wide, 30m long, downslope runoff plot, bound at the top and sides with aluminum flashing and fitted with water collecting guttering at the bottom so inputs and outputs could be quantified. The guttering fed water into a flume fixed into the ground at 4⁰ allowing water leaving the plot as runoff to be quantified.

The flumes were instrumented with a pump sampler to collect runoff samples leaving the plot and a bubbler module to measure discharge. In addition all runoff and associated sediment was collected in a covered stock tank (560 gallons for study area 1&2, 1000 gallons for study are 3). Rainfall onto the plot was measured using tipping-bucket rain gauges connected to the pump sampler. Following rainfall events all data was downloaded from the sampler using Flowlink v3.2 software.

Eroded sediment was collected from stock tank following rainfall events, coarse organic matter was removed via flotation, samples were oven dried at 60⁰C, weighed and sieved for particle size analysis using US. standard sieves at the Sevilleta LTER field station.

Setting up plots:

Plots were selected on comparable planar slopes in areas believed to be representative of endmember vegetation habitats.

Dryland environments are estimated to cover around 40% of the global land surface, and are home to approximately 2.4 billion people. Many of these areas have recently experienced extensive land degradation. This study focuses on semi-arid areas in the US Southwest, where degradation over the past 150 years has been characterized by the invasion of woody vegetation into areas previously dominated by grasslands. This vegetation change has been associated with increases in soil erosion and water quality problems, including the loss of key nutrients such as carbon from the soil to adjacent fluvial systems. Such loss of resources may impact heavily upon the amount of carbon that is lost as the land becomes more heavily degraded.

Therefore, understanding these vegetation transitions is significant both for sustainable land use and global biogeochemical cycling. This study uses an ecohydrological approach to develop an understanding of the relationship between structure and function across these transitions. This is done via the monitoring of rainfall-runoff events across instrumented runoff plots with different vegetation characteristics to investigate fluvial sediment fluxes during intense summer monsoon season rainfall events.

Keywords:

events

rain

cores

carbon

water

runoff

deserts

grasslands

grasses

vegetation

Additional Information:

This data was collected and analyzed by Alan Puttock as part of the PhD project: ‘Developing an understanding of vegetation change and fluvial carbon fluxes in semi-arid environments’. This project is supervised by Dr Richard Brazier, Dr Jenifer Dungait and Dr Kit Macleod. Analysis of samples/data is being carried out at the University of Exeter and North Wyke Research, United Kingdom.

This data was collected under USFWS permit number: 22522 10-026

Study Area 1:

Study Area Name: Grass Endmember Plot

Study Area Location: Five Points Grass core site (exact point location of plot provided below)

Single Point:

North Coordinate: 34.339186

West Coordinate: -106.728303

Study Area 2:

Study Area Name: Creosote Endmember plot

Study Area Location: Five Points Creosote core site (exact point location of plot provided below)

Each study area consisted of a 10m wide, 30m long, downslope runoff plot, bound at the top and sides with aluminum flashing and fitted with water collecting guttering at the bottom so inputs and outputs could be quantified. The guttering fed water into a flume fixed into the ground at 4⁰ allowing water leaving the plot as runoff to be quantified.

The flumes were instrumented with a pump sampler to collect runoff samples leaving the plot and a bubbler module to measure discharge. In addition all runoff and associated sediment was collected in a covered stock tank (560 gallons for study area 1&2, 1000 gallons for study are 3). Rainfall onto the plot was measured using tipping-bucket rain gauges connected to the pump sampler. Following rainfall events all data was downloaded from the sampler using Flowlink v3.2 software.

Eroded sediment was collected from stock tank following rainfall events, coarse organic matter was removed via flotation, samples were oven dried at 60⁰C, weighed and sieved for particle size analysis using US. standard sieves at the Sevilleta LTER field station.

Setting up plots:

Plots were selected on comparable planar slopes in areas believed to be representative of endmember vegetation habitats.

Dryland environments are estimated to cover around 40% of the global land surface, and are home to approximately 2.4 billion people. Many of these areas have recently experienced extensive land degradation. This study focuses on semi-arid areas in the US Southwest, where degradation over the past 150 years has been characterized by the invasion of woody vegetation into areas previously dominated by grasslands. This vegetation change has been associated with increases in soil erosion and water quality problems, including the loss of key nutrients such as carbon from the soil to adjacent fluvial systems. Such loss of resources may impact heavily upon the amount of carbon that is lost as the land becomes more heavily degraded.

Therefore, understanding these vegetation transitions is significant both for sustainable land use and global biogeochemical cycling. This study uses an ecohydrological approach to develop an understanding of the relationship between structure and function across these transitions. This is done via the monitoring of rainfall-runoff events across instrumented runoff plots with different vegetation characteristics to investigate fluvial sediment fluxes during intense summer monsoon season rainfall events.

Keywords:

events

rain

cores

carbon

water

runoff

deserts

grasslands

grasses

vegetation

Additional Information:

This data was collected and analyzed by Alan Puttock as part of the PhD project: ‘Developing an understanding of vegetation change and fluvial carbon fluxes in semi-arid environments’. This project is supervised by Dr Richard Brazier, Dr Jenifer Dungait and Dr Kit Macleod. Analysis of samples/data is being carried out at the University of Exeter and North Wyke Research, United Kingdom.

This data was collected under USFWS permit number: 22522 10-026

Study Area 1:

Study Area Name: Grass Endmember Plot

Study Area Location: Five Points Grass core site (exact point location of plot provided below)

Single Point:

North Coordinate: 34.339186

West Coordinate: -106.728303

Study Area 2:

Study Area Name: Creosote Endmember plot

Study Area Location: Five Points Creosote core site (exact point location of plot provided below)

Each study area consisted of a 10m wide, 30m long, downslope runoff plot, bound at the top and sides with aluminum flashing and fitted with water collecting guttering at the bottom so inputs and outputs could be quantified. The guttering fed water into a flume fixed into the ground at 4⁰ allowing water leaving the plot as runoff to be quantified.

The flumes were instrumented with a pump sampler to collect runoff samples leaving the plot and a bubbler module to measure discharge. In addition all runoff and associated sediment was collected in a covered stock tank (560 gallons for study area 1&2, 1000 gallons for study are 3). Rainfall onto the plot was measured using tipping-bucket rain gauges connected to the pump sampler. Following rainfall events all data was downloaded from the sampler using Flowlink v3.2 software.

Eroded sediment was collected from stock tank following rainfall events, coarse organic matter was removed via flotation, samples were oven dried at 60⁰C, weighed and sieved for particle size analysis using US. standard sieves at the Sevilleta LTER field station.

Setting up plots:

Plots were selected on comparable planar slopes in areas believed to be representative of endmember vegetation habitats.

Climate models predict that water limited regions around the world will become drier and warmer in the near future, including southwestern North America. We developed a large-scale experimental system that allows testing of the ecosystem impacts of precipitation changes. Four treatments were applied to 1600 m2 plots (40 m × 40 m), each with three replicates in a piñon pine (Pinus edulis) and juniper (Juniper monosperma) ecosystem. These species have extensive root systems, requiring large-scale manipulation to effectively alter soil water availability. Treatments consisted of: 1) irrigation plots that receive supplemental water additions, 2) drought plots that receive 55% of ambient rainfall, 3) cover-control plots that receive ambient precipitation, but allow determination of treatment infrastructure artifacts, and 4) ambient control plots. Our drought structures effectively reduced soil water potential and volumetric water content compared to the ambient, cover-control, and water addition plots. Drought and cover control plots experienced an average increase in maximum soil and air temperature at ground level of 1-4° C during the growing season compared to ambient plots, and concurrent short-term diurnal increases in maximum air temperature were also observed directly above and below plastic structures. Our drought and irrigation treatments significantly influenced tree predawn water potential, sap-flow, and net photosynthesis, with drought treatment trees exhibiting significant decreases in physiological function compared to ambient and irrigated trees. Supplemental irrigation resulted in a significant increase in both plant water potential and xylem sap-flow compared to trees in the other treatments. This experimental design effectively allows manipulation of plant water stress at the ecosystem scale, permits a wide range of drought conditions, and provides prolonged drought conditions comparable to historical droughts in the past – drought events for which wide-spread mortality in both these species was observed.

A micrometeorological station was used to document the climatic conditions at the study site. Monitoring the ambient environment in this way allowed us to more easily determine which tree growth responses were driven by changes in the native climate as opposed to those resulting from the rainfall manipulation treatments. Environmental factors such as temperature, relative humidity, and photosynthetically active radiation (PAR) have a huge impact on the physiological processes that are being explored in this project. The data collected by the station created a local climatic record which was needed to provide the context in which the treatment effects can be examined and sensor readings can be interpreted.

A CR-10X datalogger was used to record data from a micrometeorological tower centrally located in an open intercanopy area of the study site. This tower recorded precipitation with a Series 525 rain gauge (Texas Electronics, Dallas, TX), net radiation with a Kipp and Zonen NK-LITE net radiometer (Campbell Scientific, Logan, UT), photosynthetically active radiation (PAR) with a LI-190SA sensor (Li-Cor, Lincoln, NE), windspeed and direction monitored with a 05103-L R.M. Young wind monitor (Campbell Scientific, Logan, UT), and air temperature and RH% with a Vaisala HMP45C sensor. During winter months the rain gauge was fitted with a snow adaptor to thaw snow and record the total amount in mm rain. All met-station measurements were made at a height of 1-3 m above ground depending on the sensor array in question.